Microstructure and Compressive Behavior of Ti-6Al-4V Alloy Built by Electron Beam Free-Form Fabrication
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Microstructure and Compressive Behavior of Ti-6Al-4V Alloy Built by Electron Beam Free-Form Fabrication Vasiliy A. Klimenov, Vasiliy V. Fedorov, Mikhail S. Slobodyan, Natalya S. Pushilina, Irina L. Strelkova, Anatoliy A. Klopotov, and Andrey V. Batranin Submitted: 7 June 2020 / Revised: 31 August 2020 / Accepted: 23 September 2020 The paper presents the effect of layer deposition algorithms on the microstructure and the compressive behavior of the Ti-6Al-4V alloy built by the wire-feed electron beam free-form fabrication method. Patterns of the formation of pores and their shape changing under compressive loads were also investigated by computed tomography. The microstructure of the as-built samples consisted of columnar prior b grains with lengths of about several millimeters. Cross-sectional areas of the prior b grains did not depend from the metal cooling rate but were affected by the layer deposition algorithms. They were smaller and characterized by a wider range of the values when odd and even layers had been deposited perpendicular to each other. In this case, the prior b grains included predominantly the basket-weave Widmansta¨tten microstructure, while the a, a¢, and residual b phases with different volume ratios presented after the parallel layer-by-layer deposition. The only reason for this feature could be the substrate surface conditions (waviness across the deposition path). The compression test results corresponded to the formed microstructure. The sample with the maximum amount of the martensitic a¢ phase possessed the highest strength and the lowest ductility. On the contrary, the prevailed basket-weave Widmansta¨tten microstructure resulted in the improved toughness. Keywords
additive manufacturing, compressive strength, computed tomography, microhardness, microstructure, titanium alloy
1. Introduction Titanium and its alloys are widely used as a feedstock for additive manufacturing (AM) of metal products for medicine and many other applications due to their unique set of characteristics such as high strength and corrosion resistance, as well as biocompatibility with tissues of human bodies (Ref 1-13). In turn, the Ti-6Al-4V alloy is one of the most soughtafter because of its improved functional properties and good weldability enabling the layer-by-layer deposition upon the AM processes. However, the microstructure of the AM products differs significantly from other ones fabricated by conventional methods (casting, stamping, etc.). Typically, the AM Ti-6Al-4V alloy microstructure consists of columnar prior b phase grains containing the a and martensitic a¢ phases, the basket-weave Widmansta¨tten microstructure, as well as the residual b phase.
Vasiliy A. Klimenov, Vasiliy V. Fedorov, Natalya S. Pushilina, Irina L. Strelkova, and Andrey V. Batranin, National Research Tomsk Polytechnic University, 30, Lenin Avenue, Tomsk 634050, Russia; Mikhail S. Slobodyan, Institute of Strength Physics and Materials Science SB RAS, 2/4, Academic Avenue, Tomsk 634055, Russia;
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